Since an external electrode of a ceramic electronic component formed by using an electroconductive paste has been previously mounted on a circuit substrate by using solder, the surface of the above-described external electrode has been plated with Ni and, thereafter, the Ni surface has been subjected to a plating treatment with Sn/Pb and/or Sn for the purpose of improving the solder wettability and the adhesion strength to the substrate.
In recent years, demand for products which do not include Pb have increased as concerns about its environmental influence have intensified. In consideration of such circumstances, a method by using an electroconductive adhesive has been noted as a mounting method without using solder containing Pb in connection with the mounting of ceramic electronic components on circuit substrates as well.
However, it is not preferable that the mounting method using an electroconductive adhesive is applied to the external electrode which has been subjected to the plating treatment because the contact resistance between the above-described external electrode and the electroconductive adhesive is increased and the electrical characteristics are deteriorated.
Examples of external electrodes of ceramic electronic components suitable for the mounting method by using electroconductive adhesives include a technology proposed in Patent Document 1. In this technology, a base metal, e.g., Cu or Ni, is used for the first layer in consideration of the electrical connectability of the base metal to the external electrode. A noble metal, e.g., Ag, Pd, or Ag/Pd, which is resistant to oxidizing, is used as the second layer for the purpose of preventing the occurrence of a problem in that the oxidation resistance is deteriorated because no plating treatment is carried out. Furthermore, for the purpose of improving the moisture resistance, a strontium borosilicate based glass frit or the like is added to the electroconductive paste for forming the external electrode. Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-307947